028 tidbits
I haven't putzed with 028's for a long time but if my memory serves me correctly this should be fairly accurate.
028 Chronology
1) About the mid to late 70's the 028 AV's came out with a 42mm bore and a handguard instead of a working chainbrake.
2) 028 WB's came out with a 44mm bore (same as an 26, but the 028's have a shorter storke) and the early ones had a handguard whereas the later ones had a functioning chainbrake.
3) 028 Woodbosses, and AV Woodboss with came out with a 44mm bore and all of these had a functioning chainbrake.
4) 028 Supers and Super woodbosses came out with a 46mm bore (same bore as an 034). I do not believe they made any 028 Farmbosses, but i could be wrong. The 038's came out slightly before the 028's and had a different naming convenion (AV's, Supers, Farmbosses, & Magnums). The 038AV's had a 48mm bore, 038 supers and farmbosses had a 50mm bore, and the 038 magnum, mag II, ms380 have a 52mm bore.
The 028's were replaced with the 024 AV, Woodboss (42mm bore), then the 024 super, super woodboss (42mm bore, but longer stroke), and then finally the 026.
Hopefully this helps and that Lakeside chimes in with any incorrect facts that I've stated above,
Brad